Method for producing 2-azetidinone derivative

ABSTRACT

A process for producing a compound represented by the following formula (II) which comprises treating a compound represented by the following formula (I) (wherein R 1 , R 2  and R 3  represent each a specific substituent) with an enzyme capable of asymmetrically hydrolyzing an ester and the novel compound (II). The process of the present invention makes it possible to easily obtain an optically active 2-azetidinone derivative in a large amount at a low cost

TECHNICAL FIELD

This invention relates to a process for producing a 2-azetidinonederivative.

BACKGROUND ART

2-Azetidinone derivatives are important as reactive compounds forforming the subsituent at the 13-position of an anticancer compoundhaving the following structure.

As such a reactive compound, use is made of, for example, a compound (1)having the following structure (TIPS: triisopropylsilyl group, Boc:tertiary butoxycarbonyl group (hereinafter “tertiary” will beabbreviated as “t-”, i.e., “t-butoxycarbonyl group”)

This compound (1) is obtained by subjecting a racemic compound (2) (PMP:paramethoxyphenyl group (4-methoxyphenyl group), Ac: acetyl group, theacetoxy group at the 3-position and the 3-fluoro-2-pyridyl group at the4-position being in the cis-configuration):

to deprotection of Ac at the 3-position, conversion into TIPS,recrystallization, elimination of PMP at the 1-position, and separationby column chromatography (which will be sometimes abbreviated as columnhereinafter) to give: a compound (3):

followed by separation with the use of an optical resolution column andattachment of a protective group.

The process for obtaining the compound (1) from the racemic compound (2)suffers from a problem that troublesome procedures (epimerization,replacement of the solvent for recrystallization, isolation by thecolumn, etc.) are needed and yet only a low yield can be achieved. Toobtain the compound (1), there arises an additional problem that thecompound (3) should be separated by using an optical resolution columnin the step prior to the final step, which results in an increase in thecost in case of mass production.

The present invention aims at providing a production process whereby anoptically active 2-azetidinone derivative can be easily produced in alarge amount at a low cost.

DISCLOSURE OF THE INVENTION

The present inventors have found a production process whereby anoptically active 2-azetidinone derivative can be efficiently produced ina large amount at a low cost by treating a racemic 2-azetidinonederivative with an enzyme capable of asymmetrically hydrolyzing anester, thereby completing the present invention.

Accordingly, the present invention relates to a process for producing acompound represented by formula (II):

wherein R¹ represents a phenyl group or a pyridyl group (in which eachgroup may have one or more substituent(s) selected from the groupconsisting of a halogen atom, an alkyl group having 1 to 6 carbon atoms,a halogenoalkyl group having 1 to 6 carbon atoms, an alkoxyl grouphaving 1 to 6 carbon atoms, a nitro group, a carbamoyl group and a cyanogroup); R² represents a hydrogen atom, a hydroxyl group, an alkoxylgroup having 1 to 6 carbon atoms which may have substituent(s), analkanoyl group having 1 to 6 carbon atoms which may have substituent(s),an alkenoyl group having 2 to 6 carbon atoms which may havesubstituent(s), an aryl group which may have substituent(s), an aryloylgroup which may have substituent (s) or an aralkyl group which may havesubstituent(s); and R³ represents an alkyl group having 1 to 6 carbonatoms which may have substituent(s) or an alkenyl group having 2 to 6carbon atoms which may have substituent(s); which comprises treating acompound represented by formula (I) with an enzyme capable ofasymmetrically hydrolyzing an ester:

wherein R¹, R² and R³ are each as defined above.

The present invention further relates to the followings:

The above-described production process wherein R¹ is a3-fluoro-2-pyridyl group;

the above-described production process wherein R² is a a phenyl group(which may have one or more substituent(s) selected from the groupconsisting of a halogen atom, an alkyl group having 1 to 6 carbon atoms,a halogenoalkyl group having 1 to 6 carbon atoms, an alkoxyl grouphaving 1 to 6 carbon atoms, a nitro group, a carbamoyl group and a cyanogroup) or an aralkyl group (having a structure wherein an alkyl grouphaving 1 to 6 carbon atoms is substituted by one or more aryl group(s);and said aryl moiety may have one or more substituent(s) selected fromthe group consisting of a halogen atom, an alkyl group having 1 to 6carbon atoms, a halogenoalkyl group having 1 to 6 carbon atoms, analkoxyl group having 1 to 6 carbon atoms, a nitro group, a carbamoylgroup and a cyano group);

the above-described production process; wherein R² is a 4-methoxyphenylgroup or a bis (4-methoxyphenyl) methyl group;

the above-described production process wherein R³ is a methyl group;

the above-described production process wherein the enzyme is a lipase;

the above-described production process wherein the lipase is a lipaseoriginating in a microorganism belonging to the genus Pseudomonas;

the above-described production process wherein the lipase is a lipaseoriginating in a microorganism belonging to the genus Aspergillus;

the above-described production process wherein the lipase isimmobilized;

a compound represented by formula (II):

wherein R¹ represents a phenyl group or a pyridyl group (in which eachgroup may have one or more substituent(s) selected from the groupconsisting of a halogen atom, an alkyl group having 1 to 6 carbon atoms,a halogenoalkyl group having 1 to 6 carbon atoms, an alkoxyl grouphaving 1 to 6 carbon atoms, a nitro group, a carbamoyl group and a cyanogroup); R² represents a hydrogen atom, a hydroxyl group; an alkoxylgroup having 1 to 6 carbon atoms which may have substituent(s), analkanoyl group having 1 to 6 carbon atoms which may have substituent(s),an alkenoyl group having 2 to 6 carbon atoms which may havesubstituent(s), an aryl group which may have substituent(s), an aryloylgroup which may have substituent(s) or an aralkyl group which may havesubstituent(s); and R³ represents an alkyl group having 1 to 6 carbonatoms which may have substituent(s) or an alkenyl group having 2 to 6carbon atoms which may have substituent(s);

the above-described compound wherein R¹ is a 3-fluoro-2-pyridyl group;

the above-described compound wherein R² is a phenyl group (which mayhave one or more substituent(s) selected from the group consisting of ahalogen atom, an alkyl group having 1 to 6 carbon atoms, a halogenoalkylgroup having 1 to 6 carbon atoms, an alkoxyl group having 1 to 6 carbonatoms, a nitro group, a carbamoyl group and a cyano group) or an aralkylgroup (having a structure wherein an alkyl group having 1 to 6 carbonatoms is substituted by one or more aryl group(s); and said aryl moietymay have one or more substituent(s) selected from the group consistingof a halogen atom, an alkyl group having 1 to 6 carbon atoms, ahalogenoalkyl group having 1 to 6 carbon atoms, an alkoxyl group having1 to 6 carbon atoms, a nitro group, a carbamoyl group and a cyanogroup);

the above-described compound wherein R² is a 4-methoxyphenyl group or abis(4-methoxyphenyl)methyl group;

the above-described compound wherein R³ is a methyl group, etc.

In the present invention, the compound represented by formula (I) (whichwill be called the compound (I) hereinafter and the same will apply tocompounds represented by other formulae) is treated with an enzymecapable of asymmetrically hydrolyzing an ester (which will be sometimessimply called an “enzyme” hereinafter) to thereby give the compound(II). Usually another compound (III) is formed together with thecompound (II) as shown in the following reaction scheme.

It is preferable herein that in the compound (I), the acyloxy group atthe 3-position and R¹ at the 4-position are in the cis-configuration. Inthis case, the compound (I) is a racemate having the (3R, 4S) and (3S,4R) forms, the compound (II) is in the (3R, 4S) form and the compound(III) is in the (3S, 4R) form. Since the (3S, 4R) form of the compound(I) is selectively ester-hydrolyzed by the enzyme the (3R, 4S) form ofthe compound (I), namely, the compound (II) selectively remains. In casewhere the compound (II) has crystalline nature, the compound (II) may beseparated from the mixture of the compound (II) with the compound (III)by usual recrystallization using a suitable solvent without resort to acolumn. It is advantageous that, even though R³COO at the 3-position ofthe compound (II) is ester-hydrolyzed into OH and a desired protectivegroup is introduced thereinto, the R-configuration at the 3-position andthe S-configuration at the 4-position are sustained, and even though theamino group at the 1-position is eliminated or protected, theR-configuration at the 3-position and the S-configuration at the4-psotion are sustained. Owing to these characteristics, theabove-described compound (1) can be formed without resort to opticalresolution by using a column, whereby an extremely high efficiency canbe established (see, Examples and Referential Examples).

The enzyme to be used in the present invention is not particularlyrestricted, so long as it is capable of stereo-selectively hydrolyzingthe ester bond at the 3-position of the (3S, 4R) form of the compound(I).

A higher optical purity of the compound (III) obtained by theabove-described reaction brings about the higher ester hydrolysisselectivity of the (3S, 4R) form of the compound (I). Therefore, it isfavorable to employ such an enzyme.

It is preferable that the enzyme to be used in the present invention hasan optical purity of the compound (III) of 80% ee or above, stillpreferably 90% ee or above and particularly preferably 95% ee or above.

As the enzyme to be used in the present invention, a lipase ispreferable. It is still preferable to use a lipase originating in amicroorganism, for example, a lipase originating in a microorganismbelonging to the genus Pseudomonas or Aspergillus.

It is also preferable to use an immobilized lipase. Examples thereofinclude lipases immobilized on ceramics or diatomaceous earth.

As specific examples of the lipase, Amano PS, Amano PS-CI, Amano PS-DIand Amano AK (manufactured by Amano Enzyme), etc. may be cited.

To treat the compound (I) with the above-described enzyme, it isrequired to bring the compound (I) into contact with the enzyme.Although the contact method is not particularly restricted, it ispreferable to dissolve the compound (I) in an appropriate solvent andthen bring the enzyme into contact with the compound (I).

The contact time of bringing the above-described enzyme into contactwith the compound (I) may be properly determined to achieve the desiredhydrolysis ratio and optical purity. In the present invention, when animmobilized lipase is used as the enzyme, the reaction can proceed evenif the contact time with the compound (I) is a short time.Illustratively, the contact time is preferably 0.5 to 48 hours, morepreferably 0.5 to 24 hours, and most preferably 0.5 to 18 hours.

The solvent is not particularly restricted, so long as it would notinhibit the ester-hydrolysis reaction as described above. For example,use can be made of an organic solvent such as toluene, isopropyl ether,ethyl acetate, ethanol, acetonitrile, isopropyl ether, tetrahydrofuran,acetone, or a mixture thereof with water. In case of using a mixture ofan organic solvent with water, it is preferable that the mixing ratio(by volume) of water is 5% or more but not more than 80%. In case ofusing ethanol as the organic solvent, the mixing ratio of water ispreferably adjusted to 40%.

The reaction temperature may be properly determined depending on thesolvent. Namely, the reaction temperature is preferably controlled toabout 40° C. in case of using an ethyl acetate or toluene-based solvent,or to about 25° C. in case of using an ethanol-based solvent.

Stirring may be performed by using a stirrer, stirring blades, a shakeror the like. An adequate device may be suitably selected.

The relation between the concentration of the substrate, i.e., thecompound (I) and the amount of the enzyme may be suitably controlled. Ingeneral, the selectivity of the enzyme would be lowered with an increasein the substrate concentration. Also, the selectively would be loweredwith a decrease in the enzyme amount. It is preferable to control thesubstrate concentration to about 5% and the enzyme amount to about 0.4(enzyme mass/substrate mass).

The pH of the reaction system is usually adjusted to the optimum pHvalue of the enzyme during the reaction. In the present invention, theinitial pH value little differs from the pH value after the completionof the reaction. Thus, there arises a merit that no pH control isneeded.

After the completion of the enzymatic reaction, the enzyme is filteredoff and the solvent is concentrated under reduced pressure. Then theresidue is extracted with a solvent, concentrated under reduced pressureand recrystallized from an appropriate solvent. Thus, the compound (II)can be obtained at a high purity (99% or above) and a high opticalpurity (99% ee or above).

Water-containing methanol is preferable as the solvent forcrystallization. In particular, a methanol/water mixture (17:19 byvolume) is preferable therefor.

The compound (II) thus obtained is a novel optically active compound.

In the compound (I) and the compound (II), the substituents R¹, R² andR³ remain unchanged after the reaction.

Next, the substituents R¹, R² and R³ will be illustrated in greaterdetail.

R¹ represents a phenyl group or a pyridyl group which may respectivelyhave one or more substituent(s) selected from the group consisting of ahalogen atom, an alkyl group having 1 to 6 carbon atoms, a halogenoalkylgroup having 1 to 6 carbon atoms, an alkoxyl group having 1 to 6 carbonatoms, a nitro group, a carbamoyl group and a cyano group, preferably ahalogen atom or an alkoxyl group.

It is particularly preferable that R¹ is a 3-fluoro-2-pyridyl group.

R² represents a hydrogen atom, a hydroxyl group, an alkoxyl group having1 to 6 carbon atoms which may have substituent(s), an alkanoyl grouphaving 1 to 6 carbon atoms which may have substituent(s), an alkenoylgroup having 2 to 6 carbon atoms which may have substituent(s), an arylgroup which may have substituent(s), an aryloyl group which may havesubstituent(s) or an aralkyl group which may have substituent(s).

It is preferable that R² is a phenyl group or an aralkyl group. Thephenyl group may have one or more substituent(s) selected from the groupconsisting of a halogen atom, an alkyl group having 1 to 6 carbon atoms,a halogenoalkyl group having 1 to 6 carbon atoms, an alkoxyl grouphaving 1 to 6 carbon atoms, a nitro group, a carbamoyl group and a cyanogroup, preferably an alkoxyl group. The aralkyl group has a structurewherein an alkyl group having 1 to 6 carbon atoms is substituted by oneor more aryl group(s), and the aryl moiety may have one or moreSubstituent(s) selected from the group consisting of a halogen atom, analkyl group having 1 to 6 carbon atoms, a halogenoalkyl group having 1to 6 carbon atoms, an alkoxyl group having 1 to 6 carbon atoms, a nitrogroup, a carbamoyl group and a cyano group.

It is particularly preferable that R² is a 4-methoxyphenyl group or abis(4-methoxyphenyl)methyl group.

R³ represents an alkyl group having 1 to 6 carbon atoms which may havesubstituent(s) or an alkenyl group having 2 to 6 carbon atoms which mayhave substituent(s). It is particularly preferable that R³ is a methylgroup.

BEST MODE FOR CARRYING OUT THE INVENTION

Now, the present invention will be described in greater detail byreference to the following Examples, but the present invention shouldnot be construed as being limited thereto.

Optical purity was determined under the following conditions.

-   -   Column: ULTRON ES-OVM (150 mm×4.6 mmφ), Shinwa Kako    -   Mobile phase: MeOH:0.02M phosphate buffer pH 7.0=5:95    -   Flow rate: 1.0 ml/min    -   Temperature: 40° C.    -   Detection: 254 nm    -   Retention time: desired (3R, 4S) ester: 17 min, (3S, 4R) ester:        11 min, (3R, 4S) alcohol: 8.3 min, (3R, 4S) alcohol: 9.3 min,        trans-alcohol: 11, 31 min

EXAMPLE 1 (3R,4S)-cis-3-acetoxy-4-(3-fluoro-2-pyridyl)-1-(4-methoxyphenyl)-2-azetidinone

Cis-3-acetoxy-4-(3-fluoro-2-pyridyl)-1-(4-methoxyphenyl)-2-azetidinone(480 g) was suspended in a mixture of ethanol (5.76 l) with 0.1 Mphosphate buffer pH 7.0 (3.84 l). Then an enzyme Lipase PS-CI (144 g)was added thereto and the mixture was stirred at 25° C. for 16 hours.After evaporating ethanol, the residue was extracted with methylenechloride and the organic layer was evaporated. To the obtained residuewere added methanol (8.16 l) and water (9.18 l) and the mixture wasstirred at 10° C. for 16 hours. The crystals thus precipitated werecollected by filtration and dried under reduced pressure to thereby givethe title compound (182 g, 99.7% ee) as pale brown crystals.

¹H-NMR (CDCl₃) δ: 1.80 (s, 3H), 3.74 (s, 3H), 5.72 (d, 1H, J=5.6 Hz),6.09 (d, 1H, J=5.1 Hz), 6.77–6.83 (m, 2H), 7.21–7.29 (m, 2H), 7.30–7.33(m, 1H), 7.41–7.46 (m, 1H), 8.43–8.46 (m, 1H)

EXAMPLE 1a (3R,4S)-cis-3-acetoxy-4-(3-fluoro-2-pyridyl)-1-(4-methoxyphenyl)-2-azetidinone

Cis-3-acetoxy-4-(3-fluoro-2-pyridyl)-1-(4-methoxyphenyl)-2-azetidinone(1 g) was suspended in a mixture of ethanol (6 ml) with 0.1 M phosphatebuffer pH 7.0 (4 ml). Then an enzyme Lipase PS-CI (1 g) was addedthereto and the mixture was stirred at 25° C. for 30 minutes. Afterevaporating ethanol, the residue was extracted with methylene chlorideand the organic layer was evaporated. To the obtained residue were addedmethanol (17 ml) and water (19 ml) and the mixture was stirred at 10° C.for 16 hours. The crystals thus precipitated were collected byfiltration and dried under reduced pressure to thereby give the titlecompound (400 mg, 99.9% ee) as pale brown crystals. The ¹H-NMR data ofthis product was identical with those of the compound obtained inExample 1.

EXAMPLES 2 TO 14

Reactions were carried out as in Example 1 but employing differentenzymes and reaction solvents in the asymmetric hydrolysis reaction.

TABLE 1 Optical Purity of Reaction Solvent Compound (III) Reaction Ex.Enzyme (water content: 5%) (% ee) Ratio 2 Amano toluene >95 >48 PS 3Amano isopropyl ether 92 42 PS 4 Amano ethyl acetate >95 >48 PS-CI 5Amano toluene >95 >48 PS-CI 6 Amano ethanol >95 >48 PS-CI 7 Amanoacetonitrile >95 36 PS-CI 8 Amano isopropyl ether 93 32 PS-CI 9 Amanotetrahydrofuran >95 37 PS-CI 10 Amano acetone 93 29 PS-CI 11 Amanotoluene 93 26 PS-DI 12 Amano ethanol 93 22 PS-DI 13 Amano isopropylether 91 28 PS-DI 14 Amano isopropyl ether 91 35 AK

EXAMPLE 15(3R,4S)-cis-3-acetoxy-4-(3-fluoro-2-pyridyl)-1-{bis(4-methoxyphenyl)methyl}-2-azetidinone

Cis-3-acetoxy-4-(3-fluoro-2-pyridyl)-1-{bis(4-methoxyphenyl)methyl}-2-azetidinone(200 mg) was suspended in a mixture of N,N-dimethylformamide (2 ml) with0.1 M phosphate buffer pH 7.0 (18 ml). Then an enzyme Lipase PS-CI (200mg) was added thereto and the mixture was stirred at 25° C. for 2 days.Then the liquid reaction mixture was extracted with methylene chloride.The organic layer was washed with water and dried over anhydrousmagnesium sulfate. After evaporating the solvent, the obtained residuewas subjected to silica gel column to thereby give the title compound(90 mg, 99.7% ee) as a colorless oily product. Also,(3S,4R)-cis-3-hydroxy-4-(3-fluoro-2-pyridyl)-1-{bis(4-methoxyphenyl)methyl}-2-azetidinone(96 mg, 99.5% ee) was obtained.

¹H-NMR (CDCl₃) δ: 1.75 (s, 3H), 3.72 (s, 3H), 3.79 (s, 3H), 5.30 (d, 1H,J=5 Hz), 5.91 (s, 1H), 5.93 (d, 1H, J=5 Hz), 6.64 (d, 2H, J=8.9 Hz),6.83 (d, 2H, J=8.9 Hz), 7.06–7.20 (m, 6H), 8.35–8.42 (m, 1H)

Referential Example 1N-[(E)-(3-fluoro-2-pyridyl)methylidene]-4-methoxyaniline

3-Fluoro-2-formylpyridine (229 g) and paraanisidine (225 g) weredissolved in toluene (2.29 l). After adding anhydrous sodium sulfate(334 g), the mixture was stirred at room temperature for 1 hour. Afterfiltering off the insoluble matters, the liquid reaction mixture wasconcentrated under reduced pressure to thereby give the title compound(449 g).

¹H-NMR (CDCl₃) δ: 3.85 (s, 3H), 6.96 (d, J=8.9 Hz, 2H), 7.41 (d, J=8.9Hz, 2H), 7.36–7.43 (m, 1H), 7.53 (m, 1H), 8.62 (d, J=4.3 Hz, 1H), 8.86(s, 1H)

Referential Example 2Cis-3-acetoxy-4-(3-fluoro-2-pyridyl)-1-(4-methoxyphenyl)-2-azetidinone

A solution (2.29 l) ofN-[(E)-(3-fluoro-2-pyridyl)methylidene]-4-methoxyaniline (449 g) andtriethylamine (204 g) in dichloromethane was cooled to −10° C. Thenacetoxyacetyl chloride (250 g) was added dropwise thereinto and theresultant mixture was stirred at the same temperature for 30 minutes.Then it was heated to room temperature and stirred for 16 hours. Theliquid reaction mixture was washed with water and the solvent wasconcentrated under reduced pressure to thereby give a crude product (723g). This crude product was recrystallized from a solvent mixture ofethanol (6.9 l) and ethyl acetate (350 ml) to thereby give the titlecompound (486 g) as brown crystals.

¹H-NMR (CDCl₃) δ: 1.80 (s, 3H), 3.74 (s, 3H), 5.72 (d, 1H, J=5.6 Hz),6.09 (d, 1H, J=5.1 Hz), 6.77–6.83 (m, 2H), 7.21–7.29 (m, 2H), 7.30–7.33(m, 1H), 7.41–7.46 (m, 1H), 8.43–8.46 (m, 1H).

Referential Example 3Cis-3-acetoxy-4-(3-fluoro-2-pyridyl)-1-{bis(4-methoxyphenyl)methyl}-2-azetidinone

Under a nitrogen gas stream, 3-fluoro-2-formylpyridine (6.2 g) andbis(4-methoxyphenyl)methylamine (12 g) were dissolved in toluene (30ml). After adding anhydrous sodium sulfate (12 g), the resultant mixturewas stirred at room temperature for 30 minutes. After filtering off theinsoluble matters, the liquid reaction mixture was concentrated underreduced pressure to give an imine compound. A solution (60 ml) of theimine compound thus obtained and triethylamine (8.2 ml) indichloromethane was cooled to −5° C. Then acetoxyacetyl chloride (6.3ml) was added dropwise thereinto and the resultant mixture was stirredat the same temperature for 30 minutes. Then it was heated to roomtemperature and stirred for 16 hours. The liquid reaction mixture waswashed with water and then extracted with chloroform. The organic layerswere combined, washed with water and dried over anhydrous magnesiumsulfate. After concentrating the solvent under reduced pressure, ethylacetate (20 ml) and diisopropyl ether (60 ml) were added to the obtainedresidue. The resultant mixture was stirred at room temperature. Thecrystals thus precipitated were collected by filtration to thereby givethe title compound (21.8 g) as white crystals.

¹H-NMR (CDCl₃) δ: 1.75 (s, 3H), 3.72 (s, 3H), 3.79 (s, 3H), 5.30 (d, 1H,J=5 Hz), 5.91 (s, 1H), 5.93 (d, 1H, J=5 Hz), 6.64 (d, 2H, J=8.9 Hz),6.83 (d, 2H, J=8.9 Hz), 7.06–7.20 (m, 6H), 8.35–8.42 (m, 1H)

Referential Example 4 (3R,4S)-cis-3-hydroxy-4-(3-fluoro-2-pyridyl)-1-(4-methoxyphenyl)-2-azetidinone

(3R,4S)-cis-3-acetoxy-4-(3-fluoro-2-pyridyl)-1-(4-methoxyphenyl)-2-azetidinone(181 g, 99.7% ee) was dissolved in a solvent mixture of methylenechloride (725 ml) and methanol (725 ml). After adding potassiumcarbonate (5.43 g) at 0° C., the resultant mixture was stirred at thesame temperature for 1 hour. Then Dowex 50 (27 g) was added to theliquid reaction mixture followed by stirring. After filtering off theinsoluble matters, the solvent was evaporated. Then toluene was added tothe obtained residue and the mixture was azeotropically distilled. Thus,the title compound (157.9 g, 99.7% ee) was obtained as white crystals.

¹H-NMR (CDCl₃) δ: 3.74 (s, 3H), 5.34 (d, 1H, J=5 Hz), 5.62 (dd, 1H, J=5,1 Hz), 6.78–6.81 (m, 2H), 7.15–7.38 (m, 3H), 7.52–7.59 (m, 1H),8.45–8.47 (m, 1H)

Referential Example 5 (3R,4S)-cis-4-(3-fluoro-2-pyridyl)-1-(4-methoxyphenyl)-3-triisopropylsilyloxy-2-azetidinone

(3R,4S)-cis-3-hydroxy-4-(3-fluoro-2-pyridyl)-1-(4-methoxyphenyl)-2-azetidinone(126.5 g, 99.7% ee) was dissolved in methylene chloride (1.45 l). Afteradding triisopropylsilyl chloride (118 g) and imidazole (75 g), theresultant mixture was stirred at room temperature for 12 hours. Afterwashing with water, the liquid reaction mixture was dried over anhydrousmagnesium sulfate. Then the solvent was evaporated and n-hexane wasadded to the obtained residue. The mixture was stirred at roomtemperature for 2 hours and then at 0° C. for 2 hours. The crystals thusprecipitated were collected by filtration. Thus, the title compound (176g, 99.7% ee) was obtained as white crystals.

¹H-NMR (CDCl₃) δ: 0.91–1.06 (m, 21H), 3.74 (s, 3H), 5.38 (d, 1H, J=5.1Hz), 5.50 (d, 1H, J=4.9 Hz), 6.78–6.81 (m, 2H), 7.23–7.30 (m, 3H),7.35–7.39 (m, 1H), 8.41–8.43 (m, 1H).

Referential Example 6 (3R,4S)-cis-3-hydroxy-4-(3-fluoro-2-pyridyl)-1-{bis(4-methoxyphenyl)methyl}-2-azetidinone

(3R,4S)-cis-3-acetoxy-4-(3-fluoro-2-pyridyl)-1-{bis(4-methoxyphenyl)methyl}-2-azetidinone(90 mg, 99.5.% ee) was dissolved in a solvent mixture of tetrahydrofuran(0.3 ml), methanol (0.3 ml) and methylene chloride (0.3 ml). Afteradding potassium carbonate (2.3 mg), the resultant mixture was stirredat 0° C. for 1 hour and 30 minutes. Then Dowex 50 (10 mg) was added tothe liquid reaction mixture followed by stirring for 5 minutes. Afterfiltering off the insoluble matters, the solvent was evaporated. Thus,the title compound (81.6 mg, 99.5% ee) was obtained as a colorless oilyproduct.

¹H-NMR (CDCl₃) δ: 3.70 (s, 3H), 3.81 (s, 3H), 5.08–5.27 (m, 2H), 5.94(s, 1H), 6.55 (d, 2H, J=8.6 Hz), 6.85 (d, 2H, J=8.6 Hz), 7.15–7.20 (m,6H), 8.36–8.41 (m, 1H)

Referential Example 7 (3R,4S)-cis-4-(3-fluoro-2-pyridyl)-1-{bis(4-methoxyphenyl)methyl}-3-triisopropylsilyloxy-2-azetidinone

(3R,4S)-cis-3-hydroxy-4-(3-fluoro-2-pyridyl)-1-(bis(4-methoxyphenyl)methyl)-2-azetidinone(81.6 mg, 99.5% ee) was dissolved in methylene chloride (1 ml). Afteradding triisopropylsilyl chloride (55.3 μl) and imidazole (20.4 mg), theresultant mixture was stirred at room temperature for 16 hours. Afterwashing with water, the liquid reaction mixture was dried over anhydrousmagnesium sulfate. Then the solvent was evaporated. Thus, the titlecompound (112.8 mg, 99.5% ee) was obtained as a colorless oily product.

¹H-NMR (CDCl₃) δ: 0.62–1.00 (m, 21H), 3.69 (s, 3H), 3.78 (s, 3H), 5.15(d, 1H, J=5 Hz), 5.29 (d, 2H, J=5 Hz), 5.93 (s, 1H), 6.62 (d, 2H, J=8.6Hz), 6.84 (d, 2H, J=8.6 Hz), 7.05–7.19 (m, 3H), 8.31–8.34 (m, 1H)

Referential Example 8 (3R,4S)-cis-4-(3-fluoro-2-pyridyl)-3-triisopropylsilyloxy-2-azetidinone

(3R,4S)-cis-4-(3-fluoro-2-pyridyl)-1-(4-methoxyphenyl)-3-triisopropylsilyloxy-2-azetidinone(167 g, 99.7% ee) was dissolved in acetonitrile (5 l) and then cooled to−10° C. After adding an aqueous solution. (5 l) of ammonium ceriumnitrate (515 g), the resultant mixture was stirred at the sametemperature for 30 minutes. After adding diisopropyl ether, the liquidreaction mixture was washed with water, a 4% aqueous sodium thiosulfatesolution and a 2% aqueous sodium hydrogencarbonate solution. Afterevaporating the solvent, the obtained residue was dissolved in methanol(1.67 l). Then active carbon (167 g) was added and the resultant mixturewas stirred at room temperature for 16 hours. After filtering off theactive carbon, the solvent was evaporated. To the obtained residue wereadded ethanol (835 ml) and water (1.25 l). Then the mixture was stirredat room temperature for 5 hours. The crystals thus precipitated werecollected by filtration to thereby give the title compound (97.5 g,99.7% ee) as white crystals.

¹H-NMR (CDCl₃) δ: 0.89–1.08 (m, 21H), 5.71 (dd, 1H, J=4.8, 1.4 Hz), 5.35(dd, 1H, J=4.9, 1.5 Hz), 6.18 (brs, 1H), 7.22–7.26 (m, 1H), 7.33–7.41(m, 1H), 8.42–8.44 (m, 1H)

Referential Example 9 (3R,4S)-cis-4-(3-fluoro-2-pyridyl)-3-triisopropylsilyloxy-2-azetidinone

(3R,4S)-cis-4-(3-fluoro-2-pyridyl)-1-{bis(4-methoxyphenyl)methyl}-3-triisopropylsilyloxy-2-azetidinone(112.8 mg, 99.5% ee) was dissolved in acetonitrile (0.56 ml) and thencooled to −10° C. After adding an aqueous solution (4 ml) of ammoniumcerium nitrate (346 mg), the resultant mixture was stirred at the sametemperature for 30 minutes. After adding chloroform, the liquid reactionmixture was washed with water and dried over anhydrous magnesiumsulfate. After evaporating the solvent, the obtained residue wassubjected to silica gel column chromatography to thereby give the titlecompound (59.2 mg, 99.5% ee) as white crystals. The ¹H-NMR data of thisproduct was identical with those obtained in Referential Example 8.

Referential Example 10 (3R,4S)-cis-1-(t-butoxycarbonyl)-4-(3-fluoro-2-pyridyl)-3-triisopropylsilyloxy-2-azetidinone

(3R,4S)-cis-4-(3-fluoro-2-pyridyl)-3-triisopropylsilyloxy-2-azetidinone(44.9 g, 99.7% ee) was dissolved in tetrahydrofuran (448.6 ml). Afteradding 4-dimethylaminopyridine (1.62 g) and di-t-butyl dicarbonate (36.5ml) at room temperature, the resultant mixture was stirred at the sametemperature for 1 hour. After adding n-hexane, the liquid reactionmixture was washed with a 4% aqueous sodium hydrogencarbonate solutionand water. The organic layer was dried over anhydrous magnesium sulfate.After evaporating the solvent, the title compound (58.1 g, 99.7% ee) wasobtained as a brown oily product.

¹H-NMR (CDCl₃)δ: 0.88–1.02 (21H, m), 1.44 (9H, s), 5.27 (1H, d, J=5.6Hz), 5.45 (1H, d, J=5.6 Hz), 7.23–7.28 (1H, m), 7.34–7.41 (1H, m),8.41–8.44 (1H, m)

INDUSTRIAL APPLICABILITY

According to the present invention, an optically active compound (II)can be obtained from a racemic compound (I) merely by treating thecompound (I) with an enzyme capable of asymmetrically hydrolyzing anester. Thus, the process of the present invention makes it possible toefficiently obtain the compound (II) in a large amount at a low cost.

1. A process for producing a compound represented by formula (II):

wherein R¹ represents a 3-fluoro-2-pyridyl group; R2 represents ahydrogen atom, a hydroxyl group, an alkoxyl group having 1 to 6 carbonatoms which may have substituent(s), an alkanoyl group having 1 to 6carbon atoms which may have substituent(s), an alkenoyl group having 2to 6 carbon atoms which may have substituent(s), an aryl group which mayhave substituent(s), an aryloyl group which may have substituent(s) oran aralkyl group which may have substituent(s); and R3 represents analkyl group having 1 to 6 carbon atoms which may have substituent(s) oran alkenyl group having 2 to 6 carbon atoms which may havesubstituent(s); which comprises treating a compound represented byformula (I) with an enzyme capable of asymmetrically hydrolyzing anester:

wherein R¹, R² and R³ are each as defined above.
 2. The processaccording to claim 1 wherein R² is a phenyl group (which may have one ormore substituent(s) selected from the group consisting of a halogenatom, an alkyl group having 1 to 6 carbon atoms, a halogenoalkyl grouphaving 1 to 6 carbon atoms, an alkoxyl group having 1 to 6 carbon atoms,a nitro group, a carbamoyl group and a cyano group) or an aralkyl group(having a structure wherein an alkyl group having 1 to 6 carbon atoms issubstituted by one or more aryl group(s); and said aryl moiety may haveone or more substituent(s) selected from the group consisting of ahalogen atom, an alkyl group having 1 to 6 carbon atoms, a halogenoalkylgroup having 1 to 6 carbon atoms, an alkoxyl group having 1 to 6 carbonatoms, a nitro group, a carbamoyl group and a cyano group).
 3. Theprocess according to claim 1 wherein R² is a 4-methoxyphenyl group or abis(4-methoxyphenyl)methyl group.
 4. The process according to claim 1wherein R³ is a methyl group.
 5. The process according to claim 1wherein the enzyme is a lipase.
 6. The process according to claim 5wherein the lipase is a lipase originating in a microorganism belongingto the genus Pseudomonas.
 7. The process according to claim 5 whereinthe lipase is a lipase originating in a microorganism belonging to thegenus Aspergillus.
 8. The process according to claim 6 or 7 wherein thelipase is immobilized.
 9. A compound represented by formula (II):

wherein R¹ represents a 3-fluoro-2-pyridyl group; R² represents ahydrogen atom, a hydroxyl group, an alkoxyl group having 1 to 6 carbonatoms which may have substituent(s), an alkanoyl group having 1 to 6carbon atoms which may have substituent(s), an alkenoyl group having 2to 6 carbon atoms which may have substituent(s), an aryl group which mayhave substituent(s), an aryloyl group which may have substituent(s) oran aralkyl group which may have substituent(s); and R³ represents analkyl group having 1 to 6 carbon atoms which may have substituent(s) oran alkenyl group having 2 to 6 carbon atoms which may havesubstituent(s).
 10. The compound according to claim 9 wherein R² is aphenyl group (which may have one or more substituent(s) selected fromthe group consisting of a halogen atom, an alkyl group having 1 to 6carbon atoms, a halogenoalkyl group having 1 to 6 carbon atoms, analkoxyl group having 1 to 6 carbon atoms, a nitro group, a carbamoylgroup and a cyano group) or an aralkyl group (having a structure whereinan alkyl group having 1 to 6 carbon atoms is substituted by one or morearyl group(s); and said aryl moiety may have one or more substituent(s)selected from the group consisting of a halogen atom, an alkyl grouphaving 1 to 6 carbon atoms, a halogenoalkyl group having 1 to 6 carbonatoms, an alkoxyl group having 1 to 6 carbon atoms, a nitro group, acarbamoyl group and a cyano group).
 11. The compound according to claim9 wherein R² is a 4-methoxyphenyl group or bis(4-methoxyphenyl)methylgroup.
 12. The compound according to claim 9 wherein R³ is a methylgroup.